Research Interests

The common theme of Kowalewski group research is the self-organization of macromolecules, with the emphasis on the role that it can play in new nanostructured materials. Our work is highly interdisciplinary, and spans the range from molecular design, synthesis, through structure-properties studies to fabrication and characterization of devices. Major long-term projects currently underway in the group include: novel nanostructured carbons ("porous nanographenes") derived from block copolymer precursors; structure-transport properties relationships in semiconducting polymers and organic photovoltaics, and nanostructured polymer networks. The group is also actively involved in the application and development of proximal probe techniques, especially atomic force microscopy (AFM), to structure-property studies of materials and to manipulation of matter at the nanoscale level.

Porous nanographenes for energy storage

This work relies on the use of macromolecular carbon precursors, which through the process of self-assembly and directed self-assembly organize into well-defined nanoscale morphologies.1-5 After their nanostructure is fixed through chemical crosslinking, these materials are converted into porous nanocarbons with morphology resembling that of the starting material. Control over the nanoscale morphology opens the way to control of electronic structure by restricting the spatial extent of nanographitic domains, and, what is of particular importance, assuring their edge-on orientation with respect to the pore walls, thus guaranteeing their accessibility. Such overall morphology makes these materials particularly suitable for energy storage, especially as electrodes for supercapacitors, where they show specific capacitances per unit area far exceeding those exhibited by conventional materials.

Conducting polymers and photovoltaics

Here our primary goal is to reach the better understanding of the impact of nanoscale morphology on charge separation and transport processes in regioregular poly(3-alkylthiophenes) (rr-P3ATs) and their derivatives and in organic photovoltaic blends. Using the combination of AFM and Grazing Incidence Small Angle X-ray Scattering (GISAXS) we demonstrated that charge carrier mobilities in rr-P3ATs are dictated by the extent of organization of fibrillar nanostructures formed by π-stacking of polymer chains.7-14 The ability of narrow polydispersity rrP3ATs synthesized in McCullough laboratory to form well-defined fibrillar structures enabled us to use GISAXS patterns to recognize another particularly important aspect of molecular and nanoscale organization of polythiophene–like polymers: their intrinsic molecular and nanoscale porosity. This aspect of organization is a direct consequence of constraints imposed on intermolecular packing of polymer chains by strong interactions between rigid polymer backbones and their polydispersity. Currently we are focusing on understanding its impact on charge transport in conducting polymers, and on morphology and performance of polymer-based photovoltaics.

Nanostructured polymer networks

In this area we are collaborating with Matyjaszewski's group on exploring the impact of controlled heterogeneity on the structure and dynamics of polymer network systems. Particular emphasis is made on Lower Critical Solution Temperature (LCST) hydrogels, which upon the increase of temperature undergo a transition from a fully swollen to collapsed state. By comparing materials prepared by conventional and controlled radical polymerization we have demonstrated the impact of network heterogeneity on the extent and rate of swelling/deswelling transitions.15 We have also shown that the rate of the transition can be significantly increased by incorporation of dangling chains and use of branched architectures.16 Another group of projects in this area includes "self-healing" systems based on stars and nanogels with mobile arms, endowed with functionalities allowing for reversible breaking of inter-particle bonds.17In situ AFM methods developed in our lab make it possible to use the AFM probe to induce the mechanical damage to the sample surface and then to visualize the healing process.

Education and Appointments

Years

Position or Degree

July 2011

Professor, Carnegie Mellon University

2005–2011

Associate Professor of Chemistry, Carnegie Mellon University

2000–2005

Assistant Professor of Chemistry, Carnegie Mellon University

1994–2000

Research Assistant Professor, Washington University in St. Louis

1989–1994

Research Associate, Washington University in St. Louis

1989

Visiting Lecturer, Southern Illinois University

1988

Ph.D., Polish Academy of Sciences, Poland

1984–1988

Research Associate, Center of Molecular and Macromolecular Studies, Polish Academy of Sciences, Poland

1986

Research Fellow, Institute of Research on Polymer Rheology and Technology, Italy

1982–1984

Research Assistant, Center of Molecular and Macromolecular Studies, Polish Academy of Sciences, Poland